The present invention relates to a workpiece holder for holding annular workpieces, preferably a packet of such workpieces, in a centered manner, in particular piston rings and rings for synchronizing gears for working the inner and outer circumferential faces, the holder being of the type which includes a sleeve- or mandrel-type basic element.
German Patent No. 2,144,800 discloses a machine for automatically turning an inner groove in slotted piston rings in which the rings, which are introduced from a stack, are held under a clamping sleeve and are pressed into the clamping sleeve by a pressure ram. The rings are held axially, on the one hand by a pressure ram and, on the other hand, by an inner collar and are thus worked by means of a vertical tool spindle in the form of a double fly-cutter.
Slotted piston rings, after they have been pressed together radially, have almost identical diameters and can easily be packeted in this form and then machined. Rigid receptacles, as disclosed in German Patent No. 21 44 800, for example, can be used for packeted piston rings with almost identical diameters, but such a device cannot be used to circumferentially work packeted rings with different wall thicknesses and thus different outer and inner diameters since the rings, when they are pressed in, would warp, or their outer circumferential surfaces would not be placed against the inner circumference of the receptacles. The result is off center positioning and thus irregular machining, and this would inevitably lead to the rejection of the workpieces involved.